how exceptions works in yii

1. Let's assume that we have an application/apis/lyrics/LyricsFinder.php
class that makes an HTTP request to an API using CURL and returns song lyrics based
on its name. This is how we can use exceptions inside of it:
// create some custom exceptions to be able to catch them
// specifically if needed
// general lyrics finder exception
class LyricsFinderException extends CException {}
// used when there is a connection problem
class LyricsFinderHTTPException extends LyricsFinderException{}
class LyricsFinder
{
private $apiUrl = 'http://example.com/lyricsapi&songtitle=%s';
function getText($songTitle)
{
$url = $this->getUrl($songTitle);
$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, $url);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
$result = curl_exec($curl);
// if there is an HTTP error, we'll throw an exception
if($result===false)
{
$errorText = curl_error($curl);
curl_close($url);
throw new LyricsFinderHTTPException($errorText);
}
curl_close($curl);
return $result;
}
private function getRequestUrl($songTitle)
{
return sprintf($this->apiUrl, urlencode($songTitle));
}
}
2. As we don't know how a specific application needs to handle its API
connection, we will leave it to the application itself by throwing a custom
LyricsFinderHTTPException. This is how we can handle it in our
protected/controllers/TestController.php:
class TestController extends CController
{
public function actionIndex($song)
{
$lyric = 'Nothing was found.';
// importing api class
Yii::import('application.apis.lyrics.LyricsFinder');
$finder = new LyricsFinder();
if(!empty($song))
{
// We don't want to show user an error.
// Instead we want to apologize and
// invite him to try again later.
try {
$lyric = $finder->getText($song);
}
// we are looking for specific exception here
catch (LyricsFinderHTTPException $e)
{
echo 'Sorry, we cannot process your request. Try again
later.';
}
}
echo $lyric;
}
}
3. Another usage of Yii exceptions is the generation of different HTTP responses
by throwing CHttpException. For example, an action that displays a blog post
represented by a Post model, loaded by its ID will look like this:
class PostController extends CController
{
function actionView()
{
if(!isset($_GET['id']))
// If there is no post ID supplied, request is definitely
wrong.
// According to HTTP specification its code is 400.
throw new ChttpException(400);
// Finding a post by its ID
$post = Post::model()->findByPk($_GET['id']);
if(!$post)
// If there is no post with ID specified we'll generate
// HTTP response with code 404 Not Found.
throw new CHttpException(404);
// If everything is OK, render a post
$this->render('post', array('model' => $post));
}
}
How it works…
Yii converts all non-fatal application errors to CException automatically.
Additionally, the default exception handler raises either the onError or an onException
event. The default event handler writes a log message with error level set to error.
Additionally, if your application's YII_DEBUG constant is set to true, unhandled exception
or error will be displayed at a handy error screen. This screen includes a call stack trace, a
code area where the exception was raised, and the file and line where you can look for the
code to fix.